1. Field of the Invention
The present invention relates generally to excavation, in particular to hydraulic excavation and more particularly to hydraulic excavation combined with suction for removing liquid and dislodged matter.
2. Description of the Prior Art
Various excavation methods and equipment have heretofore been employed. Mechanical excavation devices range from simple hand tools such as picks and shovels to sophisticated earth moving equipment for scraping, trenching, drilling and otherwise excavating in various soil conditions.
Fluids have also been employed for excavation. For example, "Air-Knife" and "Water Cannon" excavation equipment is available from Briggs Technology, Inc. of Pittsburg, Pa. Hydraulic mining, trenching, dredging and digging devices for underwater applications are shown in the Jacobson U.S. Pat. No. 2,605,090; the Norman U.S. Pat. No. 4,087,981; the Kocher U.S. Pat. No. 4,412,394; and the Berti et al. U.S. Pat. No. 4,479,741. The dredging head disclosed in the Kocher '394 patent has suction capabilities so that material dislodged by its water jets can be withdrawn from the dredged area.
Large scale suction equipment is also used for removing concrete rubble dislodged by concrete water-blasters, for cleaning sewers and for other waste removal applications. Truck-mounted vacuum equipment for such applications is available from General Liquid Engineering, Inc. of Ontario, Canada.
However, the aforementioned excavation equipment and methods have disadvantages when used for certain excavation projects, such as locating buried utility cables and lines. Hand tools tend to be relatively slow and are often associated with relatively high labor costs, particularly if a relatively large volume of material must be excavated or relatively deep excavation is required. Furthermore, a hand tool may damage the utility cable or line.
Excavating with power equipment, such as backhoes and drilling machines, tends to be faster and less labor-intensive than excavating by hand, but is often attended by a greater risk of cable or line damage. Buried cables and lines are particularly susceptible to damage by backhoe operators. For this reason, excavation with a backhoe in a utility right-of-way may be impractical unless the operator has relatively accurate information on the depth and location of the subsurface line or cable. Otherwise the operator may be completely unaware that a utility line or cable has been exposed until it is severed. Severing a pipeline filled with a flammable material such as natural gas can be quite hazardous, as is severing an electrical line. Even if no personal injury results from severing a utility line or cable, property damage repair costs will often be incurred. Such repair costs may intitially be incurred by either the utility or the excavator, but either way they may be passed on to the consuming public in the form of higher utility, excavation or insurance costs.
Fiber optics telecommunications cables in particular are associated with heavy financial losses in the event they are severed. The revenue loss to a telecommunications company while its fiber optics cable is being repaired, and the cost of the repair itself, combine to impose an enormous liability on any party responsible for severing or otherwise damaging such a cable.
Fiber optics cables are normally buried in trenches along rights-of-way at depths sufficient to minimize the risk of accidental damage. However, fiber optics cables may share rights-of-way with other utility cables and lines. Servicing these utilities and lines often involve excavation in proximity to the buried fiber optic cables. The trenches may be formed with conventional trenching equipment and may be approximately three feet wide. Cable depths of approximately four to five feet are often specified, but the actual depths of the buried cables vary widely. Manholes are typically provided along the cable routes, and may occur at intervals of approximately four miles each.
When excavation work must be done in a right-of-way containing a fiber optic cable, it is often desirable to accurately determine the location of the fiber optic cable so that the excavator can avoid damaging it. However, the exact location of a cable buried between the manholes can be difficult to determine. Earth movement and settling may have shifted the cable from its original location and render it difficult to locate. Furthermore, the absence of ferrous metals and current-carrying conductive wires from a fiber optic cable can preclude or at least minimize the suitability of magnetic and current-detecting locating devices. Thus, locating buried fiber optic cables often requires physically exposing them. In this manner their locations can be determined with relative precision. Between the manholes the cable right-of-way is typically "potholed" by excavating at predetermined intervals to expose the buried cable. If only the cable location is desired, a large opening is generally unnecessary. Potholing may be accomplished with hand tools, machines or both. However, since hand tools are relatively slow and equipment use is attended by a risk of cable damage, both methods have their drawbacks. The excavation apparatus and method of the present invention address these problems.